/*
 * tsh - A tiny shell program with job control
 *
 * <Put your name and login ID here>
 * 曾意-3023244158

*/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE 1024   /* max line size */
#define MAXARGS 128    /* max args on a command line */
#define MAXJOBS 16     /* max jobs at any point in time */
#define MAXJID 1 << 16 /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /*在前台运行 running in foreground */
#define BG 2    /*在后台运行 running in background */
#define ST 3    /* stopped */

/*
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 *     至多一个作业在前台运行
 * At most 1 job can be in the FG state.
 */

/* Global variables
 *C标准库定义了一个全局变量environ,保存着环境变量
 extern引入外部文件的全局变量
 *
 * */
extern char **environ;   /* defined in libc */
char prompt[] = "tsh> "; /*命令提示符  command line prompt (DO NOT CHANGE) */
int verbose = 0;         /*如果为真，打印额外的输出 if true, print additional output */
int nextjid = 1;         /*分配下一个作业ID[1,2,3,...] next job ID to allocate */
char sbuf[MAXLINE];      /*把格式化的数据写入某个字符串 for composing sprintf messages */

struct job_t
{                          /* The job struct */
    pid_t pid;             /* 进程组ID  job PID */
    int jid;               /* 作业ID,即作业标识符 job ID [1, 2, ...] */
    int state;             /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE]; /*命令行 command line */
};
struct job_t jobs[MAXJOBS]; /*作业列表 The job list */
/* End global variables */

/* Function prototypes */
/*函数原型*/
/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv);//解析命令行参数，检查是否为前台任务
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);//初始化作业
int maxjid(struct job_t *jobs);//返回作业组中最大的作业ID
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);//向作业组中添加一个作业
int deletejob(struct job_t *jobs, pid_t pid);
pid_t fgpid(struct job_t *jobs);//返回当前前台作业的pid，没有则返回0
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid);
int pid2jid(pid_t pid);
void listjobs(struct job_t *jobs);

void usage(void);//打印使用规则
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine
 */
int main(int argc, char **argv)
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /*重定向标准错误流（stderr 文件描述符为2)
     *到标准输出流（stdout 文件描述符为1）
     *这样驱动就能得到所有输出在被连接到stdout的管道上
     *
     * Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /*解析命令行参数  Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF)
    {
        switch (c)
        {
        case 'h': /* print help message */
            usage();
            break;
        case 'v': /*输出额外的诊断信息 emit additional diagnostic info */
            verbose = 1;
            break;
        case 'p':            /* don't print a prompt */
            emit_prompt = 0; /* handy for automatic testing */
            break;
        default:
            usage();
        }
    }

    /* Install the signal handlers */
    /*安装信号处理程序*/

    /* These are the ones you will need to implement */
    Signal(SIGINT, sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler); /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler); /*停止或终止 Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler);

    /* Initialize the job list */
    initjobs(jobs);

    /* Execute the shell's read/eval loop */
    while (1)
    {

        /* Read command line */
        if (emit_prompt)
        {
            printf("%s", prompt);
            fflush(stdout); // 清楚缓存区，为了立刻看到输出的东西
        }
        if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
            // ferror返回0表示未出错，返回非0表示出错
            app_error("fgets error");
        if (feof(stdin))
        { /* End of file (ctrl-d) */
            fflush(stdout);
            exit(0);
        }

        /* 求命令行的值 Evaluate the command line */
        eval(cmdline);
        fflush(stdout);
        fflush(stdout);
    }

    exit(0); /* control never reaches here */
}

/*
 * eval - Evaluate the command line that the user has just typed in
 *
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.
 * 
 * 解析命令是内置还是其它，是前台还是后台
 */
void eval(char *cmdline)
{
    char* argv[MAXARGS];   //execve()函数的参数
    int state = UNDEF;  //工作状态，FG或BG 
    sigset_t set;
    pid_t pid;  //进程id
    // 处理输入的数据
    if(parseline(cmdline, argv) == 1)  //解析命令行，返回给argv数组
        state = BG;
    else
        state = FG;
    if(argv[0] == NULL)  //命令行为空直接返回
        return;
    // 如果不是内置命令
    if(!builtin_cmd(argv))
    {
        if(sigemptyset(&set) < 0)
            unix_error("sigemptyset error");
        if(sigaddset(&set, SIGINT) < 0 || sigaddset(&set, SIGTSTP) < 0 || sigaddset(&set, SIGCHLD) < 0)
            unix_error("sigaddset error");
        //在它派生子进程之前阻塞SIGCHLD信号，防止竞争 
        if(sigprocmask(SIG_BLOCK, &set, NULL) < 0)
            unix_error("sigprocmask error");

        if((pid = fork()) < 0)  //fork创建子进程失败 
            unix_error("fork error");
        else if(pid == 0)  //fork创建子进程
        {
            // 子进程的控制流开始
            if(sigprocmask(SIG_UNBLOCK, &set, NULL) < 0)  //解除阻塞
                unix_error("sigprocmask error");
            if(setpgid(0, 0) < 0)  //设置子进程id 
                unix_error("setpgid error");
            if(execve(argv[0], argv, environ) < 0){
                printf("%s: Command not found\n", argv[0]);
                exit(0);
            }
        }
        // 将当前进程添加进job中，无论是前台进程还是后台进程
        addjob(jobs, pid, state, cmdline);
        // 恢复受阻塞的信号 SIGINT SIGTSTP SIGCHLD
        if(sigprocmask(SIG_UNBLOCK, &set, NULL) < 0)
            unix_error("sigprocmask error");

        // 判断子进程类型并做处理
        if(state == FG)
            waitfg(pid);  //前台作业等待
        else
            printf("[%d] (%d) %s", pid2jid(pid), pid, cmdline);  //将进程id映射到job id   
    }
    return;
}

/*
 * parseline - Parse the command line and build the argv array.
 *
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.
 */
int parseline(const char *cmdline, char **argv)
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf) - 1] = ' ';   /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
        buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'')
    {
        buf++;
        delim = strchr(buf, '\'');
    }
    else
    {
        delim = strchr(buf, ' ');
    }

    while (delim)
    {
        argv[argc++] = buf;
        *delim = '\0';
        buf = delim + 1;
        while (*buf && (*buf == ' ')) /* ignore spaces */
            buf++;

        if (*buf == '\'')
        {
            buf++;
            delim = strchr(buf, '\'');
        }
        else
        {
            delim = strchr(buf, ' ');
        }
    }
    argv[argc] = NULL;

    if (argc == 0) /* ignore blank line */
        return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc - 1] == '&')) != 0)
    {
        argv[--argc] = NULL;
    }
    return bg;
}

/*
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.
 *    识别和解释内部命令：quit/fg/bg/jobs
 */

// Put your code here
int builtin_cmd(char **argv)
{
    // 如果是quit，则退出
    if (!strcmp(argv[0], "quit"))
    {
        exit(0);
    }
    // bg或者fg，执行do_fgbg函数
    else if (!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg"))
    {
        do_bgfg(argv);
        return 1;
    }
    // jobs，列出正在运行和停止的后台作业
    else if (!strcmp(argv[0], "jobs"))
    {
        listjobs(jobs);
        return 1;
    }
    else if(!strcmp(argv[0],"&"))
    {
        return 1;
    }
    /* not a builtin command */
    
    return 0;
}

/*
 * do_bgfg - Execute the builtin bg and fg commands
 */

/*
    1、区分是fg函数还是bg函数
    2、判断是使用的jid还是pid，并解析出id
    3、使用getjob函数找到该作业
    4、向该作业发送一个SIGCONT信号，用于让被停止（例如，因为接收到了 
    SIGSTOP、SIGTSTP、SIGTTIN或SIGTTOU 信号）的进程或进程组继续运行
    5、然后判断是fg命令否，是的话就用将要实现的waitfg等待该进程执行完，是bg的话输出信息
*/
// put your code here

void do_bgfg(char **argv)
{
    int num;
    struct job_t *job;
    // 没有参数的fg/bg应该被丢弃
    if(!argv[1]){  //命令行为空
        printf("%s command requires PID or %%jobid argument\n", argv[0]);
        return ;
    }
    // 检测fg/bg参数，其中%开头的数字是JobID，纯数字的是PID
    if(argv[1][0] == '%'){  //解析jid
        if((num = strtol(&argv[1][1], NULL, 10)) <= 0){
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);
	    //失败,打印错误消息
            return;
        }
        if((job = getjobjid(jobs, num)) == NULL){
            printf("%%%d: No such job\n", num);
	    //没找到对应的job
            return;
        }
    } else {
        if((num = strtol(argv[1], NULL, 10)) <= 0){
            printf("%s: argument must be a PID or %%jobid\n",argv[0]);
	    //失败,打印错误消息
            return;
        }
        if((job = getjobpid(jobs, num)) == NULL){
            printf("(%d): No such process\n", num); 
	    //没找到对应的进程
            return;
        }
    }

    if(!strcmp(argv[0], "bg")){
        // bg会启动子进程，并将其放置于后台执行
        job->state = BG;  //设置状态
        if(kill(-job->pid, SIGCONT) < 0)
	      	//采用负数发送信号到进程组
            unix_error("kill error");
        printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
    } else if(!strcmp(argv[0], "fg")) {
        job->state = FG;
      	//设置状态
        if(kill(-job->pid, SIGCONT) < 0) 
	     	//采用负数发送信号到进程组
            unix_error("kill error");
        // 当一个进程被设置为前台执行时，当前tsh应该等待该子进程结束
        waitfg(job->pid);
    } else {
        puts("do_bgfg: Internal error");
        exit(0);
    }
    return;
}


/*
 * waitfg - Block until process pid is no longer the foreground process
 */
// put your code here
void waitfg(pid_t pid)
{
    
    sigset_t mask;

    // 阻塞信号的集合
    if (sigemptyset(&mask) < 0)
    {
        unix_error("sigemptyset error");
    }
    // 阻塞信号
    // 如果前台进程没有结束
    while(fgpid(jobs)!=0){
        sigsuspend(&mask);
    }

    return;
}

/*****************
 * Signal handlers
 *****************/

/*
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.
 * 处理sigchld信号。这个信号是一个由操作系统向父进程发送的信号，用于通知父进
 * 程其子进程的状态已经改变。状态改变可能包括子进程终止、
 * 停止或者继续运行，这里我们只需要处理暂停和终止
 */
// put your code here

    /*
     waitpid(pid,statusp,options):
     参数1 pid
        pid>0:等待集合为单独的子进程，ID=pid
        pid=-1:等待集合有、由父进程所有的子进程组成
     参数2 status:
        -WIFEXITED(status):如果子进程通过调用exit或者一个返回（return）正常终止，就返回真
        -WIFSIGNALED(status):子进程因一个未被捕获的信号终止的
        -WIFSTOPPED(status):引起返回的子进程当前是停止的，返回真
     参数3 options：
        -WHOHANG:集合中任何子进程都没有终止，返回0
        -WUNTRACED:挂起进程，直到集合中的一个进程变成已终止或停止
        -WCONTINUED:挂起直到某正在运行的进程终止或等待集合中一个被停止的进程收到SIGCONT信号重新开始执行
           -WHOHANG|WUNTRACED：立即返回，如果等待集合中的子进程都没有被停止或终止，返回0；如果有一个停止或终止，返回它的PID
    */
void sigchld_handler(int sig)
{
    int status, jid;
    pid_t pid;
    struct job_t *job;

    if(verbose)
        puts("sigchld_handler: entering");

    /*
    以非阻塞方式等待所有子进程
    waitpid 参数3：
        1.     0     ： 执行waitpid时， 只有在子进程 **终止** 时才会返回。
        2. WNOHANG   : 若子进程仍然在运行，则返回0 。
                注意只有设置了这个标志，waitpid才有可能返回0
        3. WUNTRACED : 如果子进程由于传递信号而停止，则马上返回。
                只有设置了这个标志，waitpid返回时，其WIFSTOPPED(status)才有可能返回true
    */
    while((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0){

        // 如果当前这个子进程的job已经删除了，则表示有错误发生
        if((job = getjobpid(jobs, pid)) == NULL){
            printf("Lost track of (%d)\n", pid);
            return;
        }

        jid = job->jid;
        //接下来判断三种状态 
        // 如果这个子进程收到了一个暂停信号（还没退出） 
        if(WIFSTOPPED(status)){
            printf("Job [%d] (%d) stopped by signal %d\n", jid, job->pid, WSTOPSIG(status));
            job->state = ST;  //状态设为挂起 
        }
        // 如果子进程通过调用 exit 或者一个返回 (return) 正常终止
        else if(WIFEXITED(status)){
            if(deletejob(jobs, pid))
                if(verbose){
                    printf("sigchld_handler: Job [%d] (%d) deleted\n", jid, pid);
                    printf("sigchld_handler: Job [%d] (%d) terminates OK (status %d)\n", jid, pid, WEXITSTATUS(status));
                }
        }
        // 如果子进程是因为一个未被捕获的信号终止的，例如SIGKILL
        else {
            if(deletejob(jobs, pid)){  //清除进程
                if(verbose)
                    printf("sigchld_handler: Job [%d] (%d) deleted\n", jid, pid);
            }
            printf("Job [%d] (%d) terminated by signal %d\n", jid, pid, WTERMSIG(status));  //返回导致子进程终止的信号的数量
        }
    }

    if(verbose)
        puts("sigchld_handler: exiting");

    return;
}

/*
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.
 */
// out your code here
void sigint_handler(int sig)
{
    int olderrno = errno;
    pid_t pid;
    sigset_t mask_all, prev;
    sigfillset(&mask_all);
    sigprocmask(SIG_BLOCK, &mask_all, &prev);
    if((pid=fgpid(jobs))!=0){
	    //发送SIGINT给前台进程组里的所有进程
	    //前台进程组内的进程除了当前前台进程外，还包括前台进程的子进程
	    //最多只能存在一个前台进程，但前台进程组内可以存在多个进程
        sigprocmask(SIG_SETMASK, &prev, NULL);
        kill(-pid, SIGINT);
    }
    errno = olderrno;
    return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.
 */
// put your code here
void sigtstp_handler(int sig)
{
    if(verbose)
        puts("sigstp_handler: entering");
	//用fgpid(jobs)获取前台进程pid，判断当前是否有前台进程，没有则直接返回
    pid_t pid = fgpid(jobs);
    struct job_t *job = getjobpid(jobs, pid);

    if(pid){
	    //用kill(-pid,sig)函数发送SIGTSTP信号给前台进程组
        if(kill(-pid, SIGTSTP) < 0)
            unix_error("kill (tstp) error");
        if(verbose){
            printf("sigstp_handler: Job [%d] (%d) stopped\n", job->jid, pid);
        }
    }
    if(verbose)
        puts("sigstp_handler: exiting");
    return;
}
/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job)
{
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
        clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
{
    int i, max = 0;

    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].jid > max)
            max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
    int i;

    if (pid < 1)
        return 0;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid == 0)
        {
            jobs[i].pid = pid;
            jobs[i].state = state;
            jobs[i].jid = nextjid++;
            if (nextjid > MAXJOBS)
                nextjid = 1;
            strcpy(jobs[i].cmdline, cmdline);
            if (verbose)
            {
                printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
        }
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
        return 0;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid == pid)
        {
            clearjob(&jobs[i]);
            nextjid = maxjid(jobs) + 1;
            return 1;
        }
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].state == FG)
            return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
        return NULL;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].pid == pid)
            return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid)
{
    int i;

    if (jid < 1)
        return NULL;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].jid == jid)
            return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid)
{
    int i;

    if (pid < 1)
        return 0;
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].pid == pid)
        {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++)
    {
        if (jobs[i].pid != 0)
        {
            printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
            switch (jobs[i].state)
            {
            case BG:
                printf("Running ");
                break;
            case FG:
                printf("Foreground ");
                break;
            case ST:
                printf("Stopped ");
                break;
            default:
                printf("listjobs: Internal error: job[%d].state=%d ",
                       i, jobs[i].state);
            }
            printf("%s", jobs[i].cmdline);
        }
    }
}
/******************************
 * end job list helper routines
 ******************************/

/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void)
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler)
{
    struct sigaction action, old_action;

    action.sa_handler = handler;
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
        unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig)
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}

